The related applications and patents disclose various automatic transmissions which are electronically controlled and which include systems to ease the shock which occurs at the vehicle if gears are changed. Specifically, it has previously been proposed to ease the shock occurring at the vehicle if the vehicle is stationary, and the gear is in neutral (N) position, and the shift command lever is moved from N to an operating position in which the vehicle will move, for example drive (D), engaging a first gear, or reverse (R). Control systems are also known to ease the shock upon shifting of gears when the vehicle is already moving, for example upon shifting between first and second, second and third gear, or vice versa.
Decrease of the switching jolt or shock can be obtained hydraulically, for example by providing oil nozzles or relief valves in the pressure system; electronic elements, such as electronic control of friction clutches or friction elements in a transmission can also be used, the engagement of the friction elements being gradual and the rate of engagement being controlled in dependence on the deviation between a desired acceleration and actual acceleration, that is, in its extreme, a severe jolt.
U.S. Pat. No. 3,942,393 to which German Disclosure Document DE-OS No. 21 24 024 corresponds discloses a method and apparatus in which friction elements in an automatic transmission are controlled in dependence on change in engine speed. These frictional elements are, as customary, clutches and brake bands controlling engagement of various gear elements in a planetary gear drive.
It has also been proposed to control friction elements of a stepped transmission gear box in dependence on both engine speed and transmission output speed. For example, the input clutch of the gear is first engaged in dependence on a predetermined threshold value of the transmission gear speed n.sub.GO in a linear engagement motion. In a second control phase, the difference between the jolt actually occurring at the vehicle R.sub.ist, and a predetermined maximum permissible jolt R.sub.O, as well as the change of engine speed n.sub.M with respect to time, are used as control parameters. When the engine speed and the transmission output speed have approached each other to such an extent that the difference is below a predetermined speed difference .DELTA. n, then a third control parameter is superimposed on the control signal during a third control phase. These various control signals provide a relationship, with respect to time, of engine or motor speed and transmission speed which converge, if plotted on a graph, with an angle with respect to each other which may not exceed a predetermined angular value .beta..sub.s. For ease of explanation, this angle may be referred to as the speed convergence angle. In such devices, therefore, small transmission speeds which cannot be sensed easily and with sufficient accuracy, the clutch is first directly controlled and thereafter, in two further phases, control is based on a constant or fixed speed difference between gear input and gear output and, eventually, to provide for smooth complete, final engagement, by the speed convergence angle in dependence on the relative speed differences between input and output speed and their convergence.
It has also been proposed to decrease the jolt upon gear changing in an automatic transmission by sensing the switching or gear changing jolt which actually occurs although the frictional engaging elements have not been completely engaged as yet. From this initial jolt, a maximum value of the jolt to be expected is then computed, assuming that the clutch will engage completely. The time of complete engagement is likewise computed. A comparison is made with the maximum which is permissible upon gear changing. The difference between these signals is then applied as a control or command signal or command parameter to suitably control the friction engagement elements for soft or smooth or gradual engagement.
It has also been suggested to reduce the jolt in vehicles when the gear selection lever is moved from neutral (N) to a drive range (D, 1, or R) and to reduce the jolt by first engaging a higher gear, for example third gear, than the gear which would actually be used for driving, the first engagement of the higher gear being for a short period of time only. Such a system is described, for example, in co-pending application U.S. Ser. No. 869,449, filed Jan. 16, 1978, WILL et al, assigned to the assignee of the present application.
Difficulties still arise if it is desired to change a gear selection lever between neutral and a drive position at a time when the vehicle is stationary, since the jolt occurring at the vehicle cannot be sensed equally well when the vehicle is stationary as when it is already moving or rolling.